Looks like a yacht, probably 1914 because Tatiana's got her hair up.
I'm almost certain that this is from earlier than 1914 and it may be as earlier as 1912. You're right about TN having her hair...or at least it appears that way which ordinarily would make it no sooner than her 16th birthday in mid-1913. Additionally she also got typhoid during the Tercentenary celebrations earlier than year and they wound up shaving her head forcing on a wig. Her hair wasn't fully grown back even by mid-1914 as photos from that period indicate. She has more of an attractive short cut going there, whereas Olga clearly has her hair put up.
But look at her sister's particularly Anastasia and compare them to the formal photos from their 1914 sessions. AN looks much younger here and so does Olga. Marie's look was always more age "consistent" in my opinion but she still looks like a 12 or 13 year old girl (1911, '12) much more than a 14 or 15 year old (1913, '14).
Good questions though...perhaps someone can shed some light on this...